1. Field of the Invention
This invention relates generally to the field of radio communications, and more particularly to the field of antenna structures suitable for use at frequencies above 10 gigahertz (GHz).
The steadily increasing volume of radio communications being relayed via satellite has led to worsening frequency congestion. As a result, it has become necessary to utilize frequencies above 10 GHz in order to accommodate this increasing volume of radio traffic. Hence there is a need for antennae suitable for use in space at frequencies above 10 GHz.
In addition, atmospheric attenuation limits the maximum frequencies that can be utilized by surface-based radio astronomy stations to about 50 GHz. In order to avoid this limit, there is a developing interest in conducting radio astronomy operations from space rather than from the surface of the earth. To meet this need, antennae adapted for use in space at these frequencies are required.
An antenna for use at frequencies above 10 GHz generally includes a reflective dish for focusing received energy at a focal point; a receiving element for receiving the energy at the focal point; and a cable, waveguide, or other conducting means for carrying the received energy from the antenna to an amplifier or other device.
A reflective antenna dish, in order to be suitable for use in space, must satisfy numerous special constraints. Among these constraints are: (1) the dish must be light in weight; (2) it must be possible to fold the dish prior to launching from earth and then unfold it after deploying it in space; and (3) the dish must have good radio-frequency (rf) reflectivity at the desired frequency of operation.
In addition to satisfying these constraints, the dish should also be relatively impervious to large temperature changes. A satellite in the earth's shadow can cool to a temperature as low as -230 degrees Celsius; when in direct sunlight, its temperature can rise to +260 degrees Celsius. Unless the dish can resist the effects of such wide temperature swings, it will expand and contract so much that it will warp out of shape and put unacceptable stress on its supporting structure.